But the income threshold for this exclusive group changes every year, largely with the performance of the stock market, experts said.

In 2007, when times were good on Wall Street, one needed to have an adjusted gross income of more than $424,000 to get into the highest rank. But the stock market decline in recent years has helped lower that bar back to a level not seen since 2002.

"The further up you go, the wider swings you see," said Pete Sepp, spokesman for the National Taxpayers Union. "They have a great deal of wealth sunk into the markets, which can vary quite widely."

While much of the wealthy's income comes from capital gains on investments, bonuses on the job can also give people the needed boost.

These folks, many of whom work only blocks from where protesters are gathering in Zuccotti Park, made an average salary of just over $311,000 in 2009, according to the state Comptroller's Office. (This figure does not take into account certain income, losses and deductions that make up adjusted gross income.)

A separate study found that financial professionals made up about 14% of the top rank in 2005.

Executives, managers and supervisors working outside of finance accounted for 31%, the largest share, according to an analysis by Jon Bakija of Williams College, Adam Cole of the Treasury Department and Bradley Heim of Indiana University. Medical professionals came in at 15.7%, while lawyers made up 8.4%.

Over time, the Top 1% has claimed a bigger share of the income pie. In 2007, they earned 22.8% of the nation's income, more than double the amount in 1986, according to IRS data. The recession has since brought that slice down to just under 17% for 2009.

"The higher up the income distribution you go, the more your income rose and the larger the share of total income gains went to your group," said Roberton Williams, a senior fellow at the nonpartisan Tax Policy Center.

But as corporate profits and productivity have increased, workers aren't reaping the benefits, said Edward Wolff, a New York University economics professor who specializes in income inequality. That's helping spark the movement, which has spread across the country.

"There is a lot of anger and it's for a very good reason," Wolff said. "If all of the income gain goes to the top, there's not much left to go to the rest of the people."

Correction: An earlier version of this story included an incorrect timeframe for IRS income data. The most recent figures from the IRS are for 2009.